The present invention relates to a device and a method for correcting a landing position of an electron beam in a color cathode ray tube.
FIG. 8 is a diagram showing a plan view of a conventional color cathode ray tube. As shown in FIG. 8, a glass bulb 20 forming an envelope of the color cathode ray tube is mainly composed of a glass panel 1, a funnel 2, and a neck 21. Three electron beams emitted from an electron gun 3 incorporated in the neck 21 are deflected up and down and from side to side by a deflection yoke 4. The three deflected electron beams individually pass a color selection member 5 such as a shadow mask and hit predetermined positions (red, green, and blue phosphor areas) on a fluorescent screen 6 formed on an inner surface of the glass panel 1. The fluorescent screen 6 is scanned up and down and from side to side with the electron beams to display a color image.
When the electron beams pass the aperture of the color selection member 5, about 80% of the beams strike the color selection member 5, resulting in a thermal expansion of the color selection member 5. The thermal expansion of the color selection member 5, however, causes the electron beams, which have passed the aperture of the color selection member 5, to hit positions differing from the predetermined positions on the fluorescent screen 6, changing the landing positions. A change in an ambient temperature also causes the glass panel 1 to expand or shrink, changing the landing position likewise. While the color cathode ray tube is operating, the temperature of the funnel 2 also varies. This affects heat radiation of the color selection member 5, changing the amount of thermal expansion of the color selection member 5.
In the color cathode ray tube, the thermal expansion of the color selection member 5 results in a temperature drift (a positional drift of the landing position resulting from a temperature change of the color selection member 5), as described above. In addition, a change in the ambient temperature causes the glass panel 1 to expand or shrink, resulting in an environment drift (a positional drift of the landing position resulting from a temperature change of the environment). Conventional methods for correcting the above-mentioned landing position changes (drift) include a method for correcting the courses of electron beams according to changes in the ambient temperature and another method for correcting the courses of electron beams according to the brightness of the image.
The former method, however, cannot correct an extreme landing deviation as large as a single pitch, for instance. The latter method cannot improve correction accuracy because of thermal variation of the color cathode ray tube itself and the like.